/Engine/Source/Runtime/RHI/Public/DynamicRHI.h
Default fallback; will not work for non-8-bit surfaces and it's extremely slow.
virtual void RHIReadSurfaceData ( [FRHITexture](API\Runtime\RHI\FRHITexture) * Texture, FIntRect Rect, [TArray](API\Runtime\Core\Containers\TArray)< [FLinearColor](API\Runtime\Core\Math\FLinearColor) > & OutData, [FReadSurfaceDataFlags](API\Runtime\RHI\FReadSurfaceDataFlags) InFlags )